The present invention relates to a suspension system used on machines such as lawn and garden equipment, such as zero-turn radius (ZTR) mowers. Typically, ZTR mowers comprise unsuspended right and left drive wheels operably coupled to a mower frame, with at least one front caster wheel also coupled to the mower frame. However, independently-suspended right and left drive wheels for ZTR mowers have been shown in U.S. Pat. No. 5,946,893, U.S. Pat. No. 6,062,333, U.S. Pat. No. 6,170,242, U.S. Pat. No. 6,244,025, U.S. Pat. No. 6,460,318, U.S. Pat. No. 6,510,678, U.S. Pat. No. 6,857,254, and U.S. Pat. No. 7,107,746, each of which is incorporated herein by reference. These patents show several variations of independently-suspended right and left drive wheels for ZTR mowers, each embodiment including a prime mover such as an internal combustion engine, a hydraulic pump for each respective drive wheel being operably coupled to the internal combustion engine, and a hydraulic motor for each respective drive wheel being operably coupled to the respective hydraulic pumps. Both the internal combustion engine and the respective hydraulic pumps are connected to the frame of the ZTR mower in an unsuspended manner, wherein the hydraulic pumps are mechanically coupled and driven by the internal combustion engine via, for example, a belt-and-pulley system. The hydraulic pumps are then coupled to the respective hydraulic wheel motors via a series of hoses, wherein the hydraulic wheel motors are mounted on a suspension platform to allow for independent suspension of each of the drive wheels. The delivery of hydraulic fluid from the hydraulic pumps to the hydraulic wheel motors enables zero-turn radius drive capabilities, as is known in the art.
Recently, the use of hydrostatic transmissions known as hydrostatic transaxles has become prevalent in the ZTR mower industry. Hydrostatic transaxles combine the hydraulic pump and hydraulic wheel motor into a single unit, thereby simplifying and reducing the overall cost of the drive system of ZTR mowers and other hydraulically-driven devices. Typically, two hydrostatic transaxles are used, one for each drive wheel of the ZTR mower. Similar to the system described above, the hydraulic pump of the hydraulic transaxle is mechanically driven by an internal combustion engine (or similar drive unit) via a belt-and-pulley system, and the hydraulic pump in turn drives the hydraulic motor for each drive wheel. However, due to the integration of the hydraulic pump and hydraulic wheel motor into a single unit, suspension of the drive wheels on a ZTR mower utilizing hydrostatic transaxles presents several challenges. Foremost of those challenges is the variation in belt angle between the drive pulley coupled to the output shaft of the internal combustion engine and the driven pulley(s) of the hydraulic pump on the hydrostatic transaxle. If the belt angle between the drive and driven pulley(s) is too great, the belt may run off of one or more the pulleys and render the drive system inoperable. These challenges were addressed in the ZTR mower suspension system shown in commonly-owned U.S. Pub. 2013/0291508, incorporated herein by reference. However, the system shown in that publication was directed to a larger, commercial-style ZTR mower, wherein the engine (and thus power take-off) positioning was significantly behind the hydrostatic transaxles, thereby enabling the system's pulleys to be located on a suspended subframe without significant variations in belt angle that would potentially cause the belt to “jump” or run off of one or more pulleys. The component-placement advantages of this larger machine would not necessarily be present in a smaller ZTR mower.